The common causes of four-month-old babies shaking their heads from side to side in their sleep include: physiological causes, skin diseases, and vitamin D deficiency. 1. Physiological reasons: babies like to be shaken during the infant stage, which makes them feel safe, so most of the time shaking the head is a kind of self-soothing, in addition, before learning to express themselves verbally, babies often use body language to express their emotions, and shaking the baby’s head during sleep may be a kind of self-soothing, not accompanied by any other abnormality. 2. Skin diseases: If the baby has eczema or prickly heat on the head, face, occiput and neck, these rashes will produce itchy sensation, and the baby can not scratch, and can relieve the itchy sensation of the local skin by shaking the head. 3. lack of vitamin D: often accompanied by excessive sweating, easy to sleep, the baby did not regularly take vitamin D, often shaking the head may be a lack of vitamin D or calcium caused by increased excitability of the cerebral cortex. Four-month-old baby sleep around shaking head, there may be other causes, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.